There are several implausible assumptions behind the assumption that Bill Clinton, George W. Bush, or Obama could proclaim himself dictator for life. First, the military has been reduced in size to pre-World War II levels. The Navy and Air Force would be pretty much useless in imposing martial law. Army and Marine combat units remain dominated by white men from flyover country and might balk at orders to disarm Southerners, Westerners, and Midwesterners. A considerable portion of military strength is stationed overseas. Second, while the Federal civilian law enforcement agencies have increased in size, they lack a unified command. Additionally, the agencies are often rivals. Third, the vast majority of lawmen fall under local and state jurisdiction. They would be under no obligation to enforce Federal decrees and may be disinclined to do so. They might be willing to put down the occasional, cranky white separatist or "sovereign citizen" who stands out like a sore thumb. However, the local police are paid by local taxpayers and thus are unlikely to bite the hands that feed them.
America may become a dystopian, Stalinist nightmare at some future point. But as of 2016, the powers that be lack the ability to push us immediately to such a point.
Ys, sir, I agree...for now.
But in another generation or 2 or 3 if present trends continue there may be more of a quiet takeover that a largely unaware & fractured populace shrugs off while attending to whatever is their daily existence.
That will be long after I’m gone.